The purpose of this project is to conduct and coordinate interdisciplinary studies on high risk populations in order to clarify the role of genetic mechanisms and host-environmental interactions in carcinogenesis. Clinical studies of high-risk families have suggested etiologic relationships between the premalignant dysplastic nevus syndrome and cutaneous melanoma both hereditary and sporadic types. Investigative laboratory collaborations have clarified the relationship between lifestyle, subclinical immunologic perturbations and the epidemic of Kaposi's sarcoma and other disorders in male homosexuals. Seroepidemiologic study of the newly discovered candidate human leukemia retrovirus, HTLV, has defined patterns of virus infection and disease relationships. Mechanisms of host suceptibility are seen in DNA repair defects in familial melanoma, and families prone to diversity of rare cancers.